1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same.
2. Description of the Background Art
When there is manufactured a semiconductor device having a metal film formed on a main surface of a semiconductor substrate, a natural oxide film tends to be formed on a surface of the metal film. Accordingly, when a contact portion or the like is formed on the metal film having the natural oxide film formed thereon, the natural oxide film blocks conduction between the contact portion and the metal film, which inevitably exerts a substantial influence on a characteristic of the semiconductor device to be manufactured. Accordingly, there have conventionally been proposed various types of cleaning methods, processing devices and the like for removing the natural oxide film formed on the metal film and the main surface of the semiconductor substrate.
For example, Japanese Patent Laying-Open No. 02-256235 discloses a methodology of removing a natural oxide film formed on a metal film and on a main surface of a semiconductor substrate, by using a gas containing a halogen element and a basic gas. Furthermore, Japanese Patent Laying-Open No. 2003-133284 discloses a batch-type vacuum processing device provided with an upper chamber placed on an upper side and a lower chamber placed on an lower side, the upper chamber being used as a heating chamber, while the lower chamber being used as a processing chamber.
In the batch-type vacuum processing room, a hydrogen radical generated by a plasma generator is used in the processing chamber to remove the natural oxide film. Furthermore, Japanese Patent Laying-Open No. 2003-282530 discloses a dry cleaning device provided with a processing room for processing a wafer, a plasma unit activating with plasma a processing gas for processing the wafer, and a lamp heating the wafer disposed in the processing room, in which activated species of the processing gas activated by the plasma unit are supplied to the processing room to generate a by-product on the wafer, and the wafer is then heated with the lamp to remove the by-product. In the dry cleaning device, an activated mixed gas reacts with a natural oxide film formed on the wafer disposed in a reaction room, which results in a by-product, and the by-product is subjected to heat treatment for removal.
Japanese Patent Laying-Open No. 2003-324108 describes a method of manufacturing a semiconductor device, including a step of using a mixed gas of an argon gas and at least one type of fluorine-based gas selected from a group consisting of a nitrogen trifluoride gas, a hydrogen fluoride gas, a dicarbon hexafluoride gas, a carbon tetrafluoride gas, and a sulfur hexafluoride gas, to perform plasma etching to remove a natural oxide film formed on surfaces of a semiconductor substrate and a gate electrode and then to form a metal silicide film on a silicon oxide film and a gate electrode.
Japanese Patent Laying-Open Nos. 03-116727 and 2003-017422 also describe a method of removing a natural oxide film formed on a surface of a semiconductor substrate or the like by using a mixed gas as in the patent document described above. PCT National Publication No. 2001-520463 describes a device and method for processing and adjusting an etching chamber to scrub a thin, non-uniform etching residue on a wall and a component of the etching chamber.
Conventionally, there has not been recognized the phenomenon itself in which, for example, a natural oxide film formed on a top surface of a metal film formed on an impurity region of an NMOS and a natural oxide film formed on a top surface of a metal film formed on an impurity region of a PMOS have different growth rates, resulting in a difference between the formed natural oxide films. Accordingly, the above-described patent documents do not describe a methodology for removing a natural oxide film with a thickness that varies depending on its position.
For the method of removing the natural oxide film with a thickness that varies depending on its position, there may be contemplated, for example, a method of removing the natural oxide films by using a methodology of wet processing, an Ar sputter etching or the like and by setting a condition of a removal time period or the like to meet a requirement for the thicker natural oxide film.
When such a methodology is used, however, the semiconductor substrate and the metal film are overetched in a portion where the thinner natural oxide film is formed. Furthermore, if the processing time period is set to meet the requirement for the thinner natural oxide film, the thicker natural oxide film is not completely removed and remains.